Laserfiche WebLink
drainages were determined at the downstream end of the channel, so most of the reclaimed <br />• channel reach will not have to handle that large a peak flow rate. This was done to ensure that <br />the reclaimed drainage channel capacity will be adequate and conservatively designed. A <br />limiting velocity of 5.0 feet per second Ifps) was used to insure that the postmining drainage <br />channels would be nonerodible and stable. The limiting velocity was estimated from the tables <br />listed in SEDCAD4 as a vegetated channel using smooth brome as the seed mixture. Seed <br />mixtures used at Seneca II-W mimic that of smooth brome closer than the other choices. The <br />shape of the reclaimed channels was assumed to be trapezoidal with 3H:1V side slopes as a <br />worst case condition. The side slopes will be no steeper than 3H:1 V. <br />The channel bottom width was also calculated using SEDCAD+. Attachment 20-1 shows all <br />input and output information. All reclaimed stream channels will be conservatively constructed <br />to these measurements. Some drainages will also require a riprap lining for channel protection. <br />Please refer to the individual calculations for the proper riprap sizes to be utilized. Table 20-2 is <br />a summary of the postmining channel characteristics. Attachment 20-1 contains design <br />calculations and a summary for the 005 and 006 postmining channels. <br />After the watershed has been graded and the location of the drainage channel determined, the <br />channel will be constructed to the required shape. At first the channel will be untopsoiled to <br />• allow for initial stabilization. During the period when the watershed area is revegetating, the <br />drainages will be inspected for stability according to the rill and gully plan in Tab 22. <br />Maintenance or monitoring that may be necessary as a result of the inspections will be <br />submitted to CMLRD for review and, if necessary, approval. The methods used to stabilize the <br />channels could include installation of approved check dams and livestock ponds, erosion control <br />matting, riprap, and straw dikes. The reclaimed drainage channels will then be topsoiled and <br />revegetated according to Tabs 21 and 22, respectively after the channel has stabilized. The side <br />slopes of the meanders of the reclaimed drainage channels will be protected from erosion by <br />revegetation with drainage seed mix and shrub plantings according to Tab 22. Maintenance of <br />reclaimed drainage channels will be identified according to the Rill and Gully Plan in Tab 22. <br />Disturbance Area <br />The maximum extent of all areas anticipated to be disturbed by mining, facility, and access <br />construction, and all reclamation activities at Seneca II-W have been identified and are entirely <br />encompassed within the disturbance boundary as depicted on Exhibits 20-1 and 20-1A in this <br />permit application. The extent of this boundary was conservatively defined, and may include <br />areas, particularly in the vicinity of roads and impoundments, that will not be affected by any <br />• disturbance. An affected lands boundary map was not generated. The affected lands could be <br />considered the area between the disturbance boundary and the permit boundary. The area <br />within the mining disturbance boundary includes the area mined, the area upon which spoil is <br />deposited and graded, and where final highwalls have been reduced. <br />TR-45 11 Revised 3104 <br />